Method and apparatus for forming halftone images

ABSTRACT

Halftone images of an original scene are formed from halftone dots which are derived from a halftone dot character font. The halftone dot characters in the font comprise halftone dots of different sizes that correspond to different gray scale tones. The original scene to be reproduced is first dissected by taking a plurality of gray scale tonal measurements thereof. The tonal measurements are then utilized to call out from the halftone font the halftone dot characters that correspond to the tones measured. The halftone dot characters produced on a surface area a tonal density that is substantially equivalent to the density of the corresponding area in the original scene or photograph thereof.

United States Patent Crooks Apr. 23, 1974 METHOD AND APPARATUS FORFORMING tion, by Supernowicz, Vol. 12, No. 4, September,

HALFTONE IMAGES 1969, page 567. [75] Inventor: granitic Nelson Crooks,Princeton, Primary Examiner paul J. Hem

Assistant Examiner-Paul R. Woods [73] Assignee: InformationInternational, Inc., bos Attorney, Agent, r Firm-Lindenberg, Freilich &

Angeles, wasserman [22] Filed: May 17, 1971 Appl. No.: 143,795 [57]ABSTRACT US. Cl 178/6.7, 340/324, 340/1725, 178/68 Int. Cl H04n 1/22,G06f 3/14, B41b 27/00 Field of Search 340/1725, 324; 95/4.5; 178/66,6.7, 6.8

[56] References Cited UNITED STATES PATENTS 8/1969 Corson 178/6.8 X5/1966 Schubert 178/66 12/1971 Kolb et al. 95/4.5 R

Halftone images of an original scene are formed from halftone dots whichare derived from a halftone dot character font. The halftone dotcharacters in the font comprise halftone dots of different sizes thatcorrespond to different gray scale tones. The original scene to bereproduced is first dissected by taking a plurality of gray scale tonalmeasurements thereof. The tonal measurements are then utilized to callout from the halftone font the halftone clot characters that correspondto the tones measured. The halftone dot characters produced on a surfacearea a tonal density that is substantially equivalent to the density ofthe corresponding area in the original scene or photograph thereof.

4 Claims, 5 Drawing Figures I08 REGISTER I06 HO /l|2 H4 52 BINARYHORIZONTAL 92v I02 ADDER ACCUMUWOR I22 COUNTER BACON PRIIIRRY. I20 IREiIis iER co II IIi'iR DEiEgi OR ENDOFSCAN 94 IIEIIoRY E03 ENDOEIEIIRRIIIIERIEOCI BASEUNE I00 I26 REGISTER ADDRESSING I I A 1 REGIETERDETECTOR GENERATOR DEFLECHON /||6 I CONTROL 98\ gggg Eoc 9 |29\TRANSFERBIT CIRCUITS STATION END0EIIIIE GATES DETECTQ so ZERO VIDEO A f/DETECTOR COUNTER 40 I34 MOTOR 96 58 I END OF *scRrIIEosI 56 END OF LINE"ATENTEU APR 2 3 I974 SHEET 1 UF- 2 WQEOG EEWZS M20 om mm 2 NW 5228 025;E2 2255mm INVEN TOR Horatio N. Crooks ATTORNEY BACKGROUND OF THEINVENTION The printing processes commonly used in the graphic artsindustry, i.e. newspapers, books, magazines, etc., deposit a dot of inkon paper whenever it is desired to print all or a portion of an imageand deposit no ink when the absence of an image is desired. Thisall-ornothing process poses no problem when alphabetic or othercharacters are printed. However, when pictures such as photographs areprinted, the problem of representing the continuous tones, i.e. lightgradations, arises. This problem is solved by transforming thecontinuous tones of the original image into halftone images. Halftoneimages are typically produced by a large number of inked dots of varioussizes. The size of the inked dots correspond to the shades or tones tobe reproduced. When the largest dots, and the spaces on the paperbetween the dots, are made small compared with the visual acuity of thehuman eye, i.e. they are subliminal to the eye, the dots and the paperfuse visually and trick the eye into believing it is seeing variousshades of continuous tones.

Recently, there have been developed electronic photocomposing apparatus.The transformation of type composition into an electronic art greatlyincreases the speed of type composition. One such electronicphotocomposition system produces character images on the face of acathode ray tube by building up each character from a plurality ofsubstantially linear and vertical 7 scan lines that form slices of acharacter. The character SUMMARY OF THE INVENTION A halftone image isformed of a plurality of halftone dot characters. Each halftone dotcharacter may be represented by first digitally coded signals thatdefine a plurality of linear zones or slices of the halftone characterand second digitally coded signals that define the leading and trailingside bearings of the halftone characterJThe first digitally codedsignals for different half- I tone characters correspond to differenttonal gradations. A plurality of such halftone dot characters aregrouped together to form a halftone character font that is utilized tocreate a halftone image reproduction of the various tones in an originalscene.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic block diagram ofa scanner subsystem for scanning an original image;

FIG. 2 is a schematic block diagram of an electronic photocomposingsystem embodying the invention;

FIG. 3 is a graphical illustration of a halftone dot character;

FIG. 4 is a graphical illustration of a fragment of a halftone dotcharacter screening pattern; and

FIG. 5 is a graphical illustration of another type of halftone dotcharacter contemplated within the invention.

DETAILED DESCRIPTION Referring to FIG. 1, a scanner subsystem initiatesthe conversion of a continuous tone image 12 on a transparency 14 into ahalftone reproduction thereof. The transparency 14 may, for example,comprise one frame of a microfilm strip 15. A scanner 16, which may, forexample, include a cathode ray tube having an electron beam 17, producesa light spot 18 for scanning the transparency 14. The scanning spot 18is focused by a lens 19 onto the transparency 14. The scanning spot isdeflected from left to right in a series of vertical scans of apredetermined height under the control of a deflection and timingcontrol circuit 20. The predetermined height may, for example, be: equalto an alphanumeric character height or character line. The transparency14 on the film strip 15 may be stepped to the next line at the end ofscanning one line to produce an orthogonal scanning of the transparency14. Alternatively the scanning spot 18 may be deflected to scan the nextline. When one horizontal line or slice of the transparency 14 has beenscanned, the scanning spot 18 is also retraced to the left of thetransparency to scan another slice thereof.

The light penetrating through the transparency 14 is detected by a lightsensor such as a photomultiplier tube 26. It is, of course, apparentthat opaque film, or the like, may also be scanned by the scanner 16,with the reflected light from the image on the film comprising the imagesignal.

The amount or amplitude of light penetrating through the transparency l4depends on the density of the tones in the image contained on thetransparency 14. The tonal gradations of the transparency 14 causevariation in the amount of light in the image signal. The

light in the image signal is converted into a varying electronic signalby the photomultiplier tube 26 and then amplified in anamplifier 28. Theamplified image signal is integrated in an integrator 30 to derive thetonal content of a discrete area of the transparency 14. The integrator30 output is sampled periodically by a sampling gate 32 which isactivated by sampling pulses derived from the deflection and timingcontrol circuit 20. The output of the sampling gate 32 is digitized inan analog-to-digital (A/D) converter 34 and a succession of digitalnumerals corresponding to the tones on the transparency 14 is applied toan output storage circuit 36. The storage circuit 36 stores a successionof binary numbers that specifies the tonal gradations in the image onthe transparency 14. The binary numbers may be entered on magnetic tape40 by means of a magnetic tape station 38.

In the photocomposing system 50 of FIG. 2, the binary numbers areutilized to call out corresponding halftone dot characters stored in :autilization storage device or memory 52. The halftone dot characters aredisplayed on a display or imaging device 54. The displayed halftone dotcharacters are focused onto photographic film or stabilization paper 56by a focusing lens 58. The filmstrip 56 is mounted on rollers 60, whosemotion is controlled by a stepping motor 62 or other incremental advancemechanism.

The imaging device 54 may, for example, also function as the CRT scanner16 (FIG. 1) in which case the rollers 60 and motor 62 would also controlthe motion of the microfilm 15.

An enlarged view of a halftone dot character 70 from a halftone dotcharacter font that is stored in the storage device 52 is shown in FIG.3. The character 70 includes a plurality of adjacent linear zones 72 orcharacter slices of first and/or second visual states. The first visualstate may, for example, be black and the second one white as reproducedon photographic film. The different visual states define different zonalsegments in the zones. Black segments 74 are portions of scanlines wherethe electron beam in the imaging device is unblanked. Those portions ofthe scans wherein the electron beam is blanked are white segments 76 anda representative one is shown dashed in FIG. 3. Of course, in theimaging device itself, the black segments 74 are actually white on adark background. The black segments 74 overlap each other and areselected to be sufficiently numerous so that a halftone dot character ofa uniform density is formed on the photographic film. For the purposesof clarity and simplicity, such overlapping is not shown in FIG. 3. Thehalftone dot character 70 is seated on a character baseline 78.

Each character in a halftone font of characters is defined by a set ofparameters that includes an EM square 80 shown dashed in FIG. 3. Thebody size or overall set width of the halftone dot character is equal tothe sum of the halftone dot character width (CW) 82 and the leading 84and trailing 86 side bearings. The leading side bearing 84 (LSB) isdefined as the distance from the leading or left outer periphery of thehalftone dot character to the leading end of the character width.Similarly, the trailing side bearing 86 (TSB) is defined as the distancefrom the right edge of the halftone dot character to the trailing end ofthe character width. One halftone dot character is spaced from anotherhalftonedot character by the sum of the trailing and leading sidebearings, respectively, of the successive char- 'acters.

A plurality of halftone dot characters are grouped together to form ahalftone character font. Each character in the font is selected toexhibit the same sized EM square. One character in the font differs fromanother character by the length of the black segments 74 in the linearzones 72. The totality of the linear zones in a character creates asubstantially square halftone dot. Of course, curvilinear zones may alsobe utilized and shapes other than square may be formed if desired.

The halftone dot occupies a portion of the EM square such that theproportion of black to white area produces a desired tone. The halftonedot characters in a font vary from a character wherein the EM square is100 percent black to one wherein the EM square is less than percentblack. There may, for example be 64 halftone dot characters in a font.Such characters vary from lightest to the darkest to give a desiredtonal range. Of course, any other number of characters that gives thedesired tonal range in a font may be utilized. The scanner 16 in FIG. 1scans a vertical height substantially equal to an EM square 80.

' In halftone reproductions, the halftone dots of successive linespreferably are oriented at an angle of 45 in relation to each other,i.e. the centers of the halftone dots in one line are horizontallydisplaced by EM/2 relative to the centers of halftone dots in the twoadjacent lines. In FIG. 4, there are shown portions of three successivelines of halftone dot characters derived from a character font. Thecharacters 82 through 86 all exhibit 25 percent black regions or dots.It is to be noticed that the EM square, shown dashed, of the halftonecharacter 84 is positioned intermediate the characters 82 and 83 andintermediate the rows or lines containing the characters 82 and 83 and85 and 86. This causes the halftone dots of the characters 82 through 86to exhibit the usual 45 screening pattern or orientation to each otheras shown by the screening lines 87, 88 and 89.

The sizes of the EM squares of all of the halftone dot characters in afont may be selected to be substantially equal to one point. Thus, thereare 72 halftone dot characters in one inch of a line of halftonecharacters. This creates 102 screening lines per inch, which is a highgraphic quality screening.

The parameters of a halftone character, as well as other data to bedescribed below, are stored in the memory 52 shown in FIG. 2. The memory52 may, for example, comprise a magnetic core random access memory thatis divided into two main portions, a primary portion 92 and a secondaryportion 94. The primary portion 92 includes a plurality of successivestorage locations that correspond'one-to-one with the characters in ahalftone font. A second primary portion is allocated to alphanumericfonts. Thus, for a 64 character halftone font, there will be 64 storagelocations in the primary portion 92 allocated to the halftone font. Eachmultibit storage location in the primary portion 92 is addressed by acharacter identity code which comprises one of the digitized numbersderived from the analog-to-digital converter 34 (FIG. 1). Thus, adigitized tonal gradation is the character identity code of thecorresponding halftone dot character. The sequence of the addresses inthe memory 52 may begin with the address for the smallest character dotin the halftone font and continue successively up to the largestcharacter dot. The contents in each one of the multibit storagelocations of the primary portion 92 of the memory 52 is actually anaddress for the storage location in the secondary portion 94 of thememory wherein is stored the data that define the corresponding halftonecharacters. Thus, when an identity code is utilized to address ahalftone dot character in the primary portion 92 of the memory 52, thebinary number read from this memory storage location comprises anaddress in the secondary portion 94 of the memory 52 that begins a blockof secondary storage locations wherein the coded parameters of thehalftone dot character is stored successively.

The secondary portion 94 of the memory 52 stores in sequence the blocksof information necessary to create a halftone dot character pattern onthe cathode ray tube 54. The contents of the first memory location for ablock of data in the secondary portion 94 relating to one halftone dotcharacter in the memory may be a coded representation of the number ofscans in the leading side bearing (LSB) 84. The format data stored inthe next storage location may be the sum of the number of scans in thecharacter width (CW) 82 (FIG. 3) and the trailing side bearing (TSB) 86of the character. The next parameter stored is the character width (CW).The next parameter stored is the vertical displacement that defines thedisplacement of the black scans from the base line 78 of the halftonedot character. The remaining data stored for a halftone dot character isnot format data but is rather the segment data, which are the successivecoded representations of the lengths of the individual black segmentsand the individual white segments in each scan of a halftone dotcharacter.

To attain synchronism between the scanning beam reproducing the halftoneimage in the cathode ray tube 54 and the reading of the memory 52, thestored segment words also include data relating to the starting andretracing of the scanning beam 96 in the cathode ray tube 54, as well asdata relating to blanking and unblanking it. The least significant bitin a binary number defining a black segment, i.e. the 2 bit, may beselected to designate the end of a scan or retrace. No white segmentsterminate a scan because the scanning beam is retraced after finishingthe last black segment in a scanline. A binary 1" occurring in the 2 bitposition indicates that the scan retraces whereas a binary 0 indicatesthat the scan continues.

The next least significant bit in a segment word, i.e. the 2 bit,indicates when the scanning beam should be turned on, i.e. unblanked,and when the beam should be turned off, i.e. blanked. When a binary 1"is stored in this position, the beam is turned on whereas the beam isturned off when a binary 0 is stored in this position. Thus, the blacksegment words are differentiated from the white segment words by thebinary bit, i.e. the color bit, stored in this 2 bit position. It istherefore apparent that the segment words themselves control theformation of the zones or slices of the halftone dot characters.

In FIG. 2 a magnetic tape 40 that contains text material and halftoneimage material is read in a magnetic tape station 98 and the characteridentity codes of both the alphanumeric and halftone dot characters areutilized by the addressing circuits 100 to address the memory 52. For ahalftone dot character, the identity code addresses the memory 52 andthe contents of the addressed storage location are read into a dataregister 102. The data read into the data register 102 is read back intothe memory 52 to prevent destruction thereof and is also read from theregister 102 into the addressing circuit 100. This is because the firstdata read from the memory 52 is the first address in the secondaryportion 94 of the memory 52 that begins the block of data that definesthe character parameters needed to create the halftone dot character.Each secondary address is then incremented by an incrementer 104 so thateach secondary address in incremented by one as the data in the block isread from the memory 52. The first data read from the memory 52 in theblock of character parameters is the binary number representing theleading side bearing (LSB) of the character. This data is coupledthrough the data register 102 to a binary adder 106. The binary adder106 adds thecontents of the data register 102 to the contents of aregister 108. The register 108 stores the sum of the character width(CW) and the trailing side bearing (TSB) from the previous character.The sum of the data in the register 102 and in the register 108 is thehorizontal position in the cathode ray tube 54 of the start of the newcharacter to be created. At the beginning of a line, the contents oftheregister 108 is zero. The summed numher in the binary adder 106 isadded to the contents of an accumulator 110 so that the accumulativeposition of the beginning of the scans of each character is indicated.

The data contained at the next successive secondary address is a binarynumber representing the sum of the character width (CW) and the trailingside bearing (TSB) of the halftone dot character and this data is fedthrough the data register 102into the register 108. The new contents ofthe register 108 remain therein until the next character is read. At thenext character, the binary adder 106 adds the contents of the register108 (the character width and the trailing side bearing of the previouscharacter) to the leading side bearing (LSB) of that next character.This addition specifies the position to which the scanning beam is movedat the end of scanning one halftone dot character so that the beam isproperly positioned to scan the next halftone dot character.

The accumulated total in the accumulator 110 is transferred to ahorizontal counter 112. The count in the counter 112 is coupled to ahorizontal digital-toanalog converter (DACON) 114 where the'digital orbinary data is transformed to an analog voltage so as to horizontallyposition the scanning beam 96. The output of the DACON 114 is coupled tothe deflection circuit 1 16 of the tube 54 to so deflect the scanningbeam 96.

The horizontal counter 112 may, for example, comprise a binary counterfor stepping the scanning beam in the imaging device 54 across the facethereof as a line of halftone dot characters is printed.

The next data read out of the memory 52 is the number of scans in thecharacter width. (CW). This number is coupled into a scan counter 120.The scan counter is decremented by a count of one at the end of eachscanline so that when a count of zero is reached, a zero detector 122,coupled to the scan counter, signals that the end of the character hasbeen reached. The vertical displacement is read into the baselineregister 138.

The next data read from the memory 52 is the segment data that actuallycauses the halftone dot character patterns, or dots, to be written onthe cathode, ray tube 54. The segment data is read into a bufferregister 124 which register stores segment data relating to a pluralityof scanlines and may be operated in a simultaneous read-write mode, i.e.push-pull, wherein one section of the buffer register 124 is beingwritten into whereas another section is being read. Such operationprevents delay in forming the dot patterns. A bit detector 126 iscoupled to detect a binary 1 in the 2 bit position of the binary numbersentering the buffer register 124 to detect that information relating toan entire scan. The bit detector 126 activates a sawtooth generator 128when a binary 1 is detected to begin the vertical deflection ofthescanning beam. The segment data in the buffer register 124 is jamtransferred through transfer gates 129 into a video counter 130 and thevideo counter 130 is downcounted by an oscillator 132. When the count atthe video counter 130 goes to zero, a zero detector 134 transfersanother segment from the buffer register into the video counter.

Also coupled to the output of gates 129 is a dual bit detector 136 whichfunctions to decode the 2 and 2 bit positions in each segment. When abinary 1 occurs in the 2 bit position, the bit detector 136 turns on thescanning beam 96 of the cathode of cathode ray tube 54. When a binary 0"is detected in this bit position, the scanning beam is biased off. Whena binary 1 is detected in the 2 bit position, this signifies that whichthe vertical displacement or baseline position is read and stored duringthe creation of a halftone dot character. The end of scan signal is alsocoupled to upcount the count in the horizontal counter 112 to move thebeam to a new horizontal position for the next scan.

OPERATION The photocomposition system 50 produces both alphanumeric andhalftone dot character patterns on the imaging device or cathode raytube 54. These patterns are projected onto photosensitive film 56 toprovide both text and pictures. The compatibility illustrated by thesystem 50in producing both text and pictures in the same device, and ina similar manner, has not heretofore been achieved.

The operation of a photocomposition system such as the system 50 in FIG.2 in creating alphanumeric characters is explained in greater detail inU.S. Pat. No. 3,568,178, for Robert F. Day, entitled ElectronicPhotocomposition System and assigned to the same assignee as the presentapplication.

The production of pictures by means of halftone dot characters differsfrom the production of text because, of course, pictures cannot bespecified as text can, but rather must be read into the system. Thus,the scanner subsystem 10 of FIG. 1 is needed for pictures, but not fortext. Of course, in actuality the scanner 16 may be identical to theimaging device 54 and the subsystem 10 may be a part of the system 50.

To create a halftone replica of an image 12, the image 12 is firstdissected by scanning it by means of the scanner 16 and sampling theintegrated light output of the film 14. Such a sampled output providesdiscrete measurements of the tones in the image 12. The sampled tonesare converted into binary numbers by the analog-to-digital converter 34,and the storage circuit 36 merges each converted binary number into anyone of 64 halftone dot character identity codes corresponding mostclosely to the binary number. Thus, the large number of tonal numbersare mapped into 64 dot character identity codes. This limits the size-ofthe halftone font that must be stored in the photocomposition system.

The character identity codes specifying the image 12 are written ontomagnetic tape 40, and the tape 40 may be merged with text data to createa complete newspaper page of text and pictures or the like.

Instructions specifying the location of the picture on a page are alsoput onto the tape by means, not shown in the drawings. For simplicity inexplanation, it is assumed that the picture begins at one side of a pageand ends at the other side. The fragment of a halftone image shown inFIG. 4 is assumed to be the image to be reproduced.

The first identity code read from the tape 40 produces the halftone dotcharacter or tonal region 82 on the film 56. The leading side bearing(LSB) of the character 82 is read into the binary adder 106 where it issummed with the contents of the register 108. Since this is the firsthalftone dot character in a line, the contents of the register 108 iszero. Consequently, the leading side bearing of the character isaccumulated unchanged in the accumulator 110 and stored in thehorizontal counter 112. The converter (DACON) 114 converts the binarynumber to an analog signal that is coupled to the deflection circuits116 to position the scanning beam 96 horizontally.

The combined character width (CW) and trailing side bearing (TSB) ofthis first halftone character is transferred to the register 108. Thecharacter width (CW) alone is transferred to the scan counter 120. Thevertical displacement or baseline is transferred to the register 138.

The segment data that creates the halftone dot is then transferredsequentially into the buffer register 124. The bit detector 126 detectsa binary 1 in the 2 bit position of the last segment in the first scanof the halftone dot. Consequently, information relating to an entirescan is stored in the register 124. The detector 126 therefore turns onthe sawtooth generator 128 as well as transfers the first zonal segmentinto the video counter 130. Since the first zonal segment is white, thedetector 136 detects the binary 0 in the 2 bit position and does notturn on the scanning beam 96. Consequently, the video counter 130 iscounted down by the oscillator 132 while the scanning beam 96 issweeping vertically but the beam is blanked.

At the end of scanning the first white zonal segment, the zero detector134 detects the end of the downcount of the video counter 130 andinitiates the transfer of the next zonal segment, which is a blacksegment, into the video counter 130. The bit detector 136 detects thebinary 1 in the 2 bit position of the black segment word and turns onthe scanning beam 96. The detector 136 also detects the binary 1" in the2 bit position, i.e. the retrace bit, and applies an enabling signal tothe AND gate 137. The scanning beam 96 scans out the black segment whilethe video counter 130 is counted down. When the detector 134 detects theend of the black segment, the AND gate 137 is actuated to turn off thesawtooth generator 128 and retrace the scanning beam 96. The end of scansignal also advances the horizontal counter 112 by a count of one andcounts down the scan counter 120. The first segment of the next scan istransferred into the video counter 130 and a set of events similar tothe first scan occur.

By the end of scanning the zonal segment data, the scan counter isdowncounted to zero and the zero detector 122 signals the end of acharacter. The end of character signal (EOC) is applied to the tapestation 98 to read the next character identity code. The leading sidebearing (LSB) of this second halftone character is added in the binaryadder 106 to the sum of the character width (CW) and the trailing sidebearing (TSB) of the previous character. This sum is added in theaccumulator l 10 to the previous number stored therein, i.e. thebeginning of the character width of the first character, and thisinitial scanning position of the new character is transferred into thecounter 112. The scanning beam is moved to this new position and thesecond halftone dot character is created.

At the end of scanning a line of halftone dot characters, the motor 62is activated by a signal (end of line) from the tape station 98 to movethe film 56 an increment to the next line. The tape station 98 alsoprovides an even line offset signal to start the next line ofhalftonecharacters offset so as to produce a 45 screening pattern asshown in FIG. 4. Each line of halftone dot characters is therefore laiddown in a 45 screening pattern until a halftone replica of the originalimage has been created.

It is to be noted that the EM squares or character regions overlap eachother so as to insure that when 100 percent black regions are specified,there are no white areas within these regions. Such overlapping alsorenders the system 50 relatively insensitive to slight incorrectpositionings of the scanning beam or film.

In FIG. there are shown halftone characters that include two halftonedots positioned at a 45 angle to each other. Such a configurationpermits halftone replicas to be reproduced without offsetting everyother line. In FIG. 5a the halftone dots 140 create a tone less densethan the character in FIG. 5b.

Thus, there has been described apparatus for creating halftonereproductions of an original scene. The method of creating halftonereplicas of an original scene includes the steps of storing a font ofhalftone dot character signals in a storage device or memory. The

tones on an original scene are extracted from the scene and the halftonecharacters that correspond to these tones are extracted from the memoryand laid down on a surface to reproduce the original scene.

What is claimed is:

1. The method of creating on a surface a halftone reproduction of anoriginal scene comprising the steps of providing a font of electronichalftone dot character signals in digital form storing said halftone dotcharacter signals in a digital storage device providing an indication ofthe tonal gradations of said original scene that are to be reproduced onsaid surface extracting from said storage device said halftone dotcharacter signals that correspond to said tonal gradations, and

utilizing said extracted halftone dot character signals to createcorresponding halftone dots of various sizes on said surface so as toreproduce the tonal gradations of said original scene.

2. The method of claim 1 wherein said step of providing an indication ofthe tonal gradations of said original scene includes providing asequence of multibit identity codes, each different identity coderepresentative of a particular tonal gradation.

3. The method of claim 2 wherein said step of storing includes storingsaid halftone dot character signals in addressable storage locations ina first section of said storage device and storing the addresses of saidaddressable storage locations in locations in a second section of saidstorage device, each location in said second section being addressableby a different one of said identity codes.

4. A photocomposing system for producing a halftone replica of anoriginal scene comprising in combination means for scanning saidoriginal scene to derive tonal repesentations thereof digitizing meansresponsive to said scanning means for producing digital signalscorresponding to the density of said tonal representations an imagingdevice means providing a font of halftone dot characters,

each consisting of a plurality of signals that create halftone dotsonsaid imaging device a storage device for storing said signals of saidfont,

and

means responsive to said digitizing means for extracting from saidstorage device a plurality of said halftone characters corresponding tosaid digitized tonal representations to provide a substantial replica ofsaid original scene on said imaging device.

1. The method of creating on a surface a halftone reproduction of anoriginal scene comprising the steps of providing a font of electronichalftone dot character signals in digital form storing said halftone dotcharacter signals in a digital storage device providing an indication ofthe tonal gradations of said original scene that are to be reproduced onsaid surface extracting from said storage device said halftone dotcharacter signals that correspond to said tonal gradations, andutilizing said extracted halftone dot character signals to createcorresponding halftone dots of various sizes on said surface so as toreproduce the tonal gradations of said original scene.
 2. The method ofclaim 1 wherein said step of providing an indication of the tonalgradations of said original scene includes providing a sequence ofmultibit identity codes, each different identity code representative ofa particular tonal gradation.
 3. The method of claim 2 wherein said stepof storing includes storing said halftone dot character signals inaddressable storage locations in a first section of said storage deviceand storing the addresses of said addressable Storage locations inlocations in a second section of said storage device, each location insaid second section being addressable by a different one of saididentity codes.
 4. A photocomposing system for producing a halftonereplica of an original scene comprising in combination means forscanning said original scene to derive tonal repesentations thereofdigitizing means responsive to said scanning means for producing digitalsignals corresponding to the density of said tonal representations animaging device means providing a font of halftone dot characters, eachconsisting of a plurality of signals that create halftone dots on saidimaging device a storage device for storing said signals of said font,and means responsive to said digitizing means for extracting from saidstorage device a plurality of said halftone characters corresponding tosaid digitized tonal representations to provide a substantial replica ofsaid original scene on said imaging device.